Mica based,ceramic composite material

ABSTRACT

THE USE OF SYNTHETIC, FLUORINE CONTAINING MICAS, BY HOTPRESSING AS A SECOND PHASE INCORPORATION INTO A CERRAMIC BODY IN AN AMOUNT OF 5 TO 50% BY VOLUME TO PRODUCE A NOVEL PARTICULATE DISPERSION OR A DISPERSED MICRO-LAMINATE THEREBY ENHANCING THE PROPERTIES OF THE CERAMIC MATERIALS.

Aug. 6, 1974 J. w. M CAULEY MICA BASED, CERAMIC COMPOSITE MATERIAL 2 Sheets-Sheet 1 Filed May '7. 1973 w w i United States Patent once MICA BASED, CERAMIC COMPOSITE MATERIAL James W. McCauley, Wakefield, Mass., assignor to the United States of America as represented by the Secretary of the Army Filed May 7, 1973, Ser. No. 357,571 Int. Cl. B32b /16; C04b 33/26; F16k 31/12 US. Cl. 106-46 2 Claims ABSTRACT OF THE DISCLOSURE The use of synthetic, fluorine containing micas, by hotpressing as a second phase incorporation into a ceramic body in an amount of 5 to 50% by volume to produce a novel particulate dispersion or a dispersed micro-laminate thereby enhancing the properties of the ceramic materials.

The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to me for royalty thereon.

This invention relates to hot-pressed fluorine micas/ ceramic composites having improved properties.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION The present invention relates to the incorporation of a fluorine containing mica by hot-pressing into a ceramic material in an amount of 5 to 50% by volume to produce a mica-ceramic composite. Illustrative fluorine containing micas include commercially available KMg Alsi O F and BaMg Al Si O F Other synthetic fluorine containing micas considered operable are disclosed by H. R. Shell and K. H. Ivey, Fluorine Micas, Bureau of Mines Bulletin 647 (1969). Illustrative ceramic material include commercially available A1 0 MgO, 3Al O -SiO Si N SiO etc.

It is an object of the present invention to provide and disclose a novel mica-ceramic materials having controllable properties and microstructure.

It is a further object of the present invention to provide and disclose novel mica-ceramic composite materials having enhanced strength and toughness by the substantially reaction free incorporation of the mica phase.

It is a further object of the present invention to provide and disclose novel mica-ceramic composite materials hav ing enhanced thermal shock resistance.

It is a further object of the present invention to provide and disclose novel mica-ceramic composite materials which are self-lubricating.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and a fuller understanding of the invention may be ascertained by referring to the following description and claims taken in conjunction with the accompanying drawings in which:

FIG. 1 is a photomicrograph of an illustrative relief polished hot-pressed Ba-mica/Al o composite material.

FIG. 2 is a photomicrograph of an illustrative relief polished, hot-pressed Ba-mica/Al O composite material thermally shocked into room temperature water from 700 C.

3,827,892 Patented Aug. 6, 1974 FIG. 3 is a graph illustrating average values obtained from the evaluation of hot-pressed Ba-mica/Al O composties for mean Knoop (100) microhardness.

FIG. 4 is a graph illustrating values obtained from the evaluation of hot-pressed Ba-mica/Al O composites for Four Point Flexure Strengths.

FIG. 5 is a graph illustrating values obtained from the evaluation of hot-pressed Ba-mica/Al o' composites for Youngs Moduli.

DESCRIPTION OF PREFERRED EMBODIMENT In a specific example, a mixture of 57.44 grams of A1 0 by volume) having an average grain size of about 0.5 to 1.0a; and 5.6 grams of BaMg Al Si O F flakes (10% by volume) having an average flake size 30;; in length by about 5-10p. thick, were blended by tumbling the dry material in a glass container for a period of about 24 hours. After blending, the mixture is loaded into a graphite die and brought to a pressure of about 7,000 p.s.i. When the mixture is under full pressure, the graphite die and plunger assembly is inductively heated in air to 1250 C. The above pressure and temperatures are maintained for a period of about 1 hour and then terminated. When the temperature reaches 500 C., the pressure is fully released and the system allowed to cool to room temperature. A BaMg Al Si- O F /a-Al O composite material 2" in diameter by about 0.25" thick, was recovered.

Both BaMg Al Si O' F and KMg AlSi O F have been reactively hot-pressed with lZ-AI2O3 and other ceramics. Experimentally determined densities ranged from 99.5% of theoretical for the A1 0 composite to 95.5 of theoretical for the 50% A1 0 material. These data, together with microscopic examination and X-ray diffraction analysis shows that there is no reaction product formation for the higher A1 0 composites, and not more than l2% for the lower A1 0 compacts.

Normal A1 0 is hot-pressed at temperatures of about 1800 C., whereas the present micas/A1 0 composites can be fully sintered and densi-fied at 1250 C., which is more than 500 C. lower than the normal processing conditions. This is possible because the micas release, e.g., a KF vapor phase throughout the compact which acts as a fluxing agent in the hot pressing process.

FIG. 1 is a photomicrograph of a representative Bamica/Al O composite material fabricated in accordance with the present method. Coefiicient of friction measurement on these materials indicate that the microstructure is also controllable since the measured frictional properties of Ba-mica/Al O are 20-30% better than those of commercially available A1 0 FIG. 2 is a photomicrograph of a Ba-mica/Al O material thermally shocked into room temperature from 700 C. Note that the mica flakes in the composite absorb crack propagation energy by changing the crack direction and by initiating new cracks. I

FIGS. 3, 4 and 5 indicate that the physical properties of the present composite, i.e., hardness, strength and stiffness, respectively, may be controlled by the amount of fluorine containing mica incorporated into the ceramic.

The average hardness values indicated on FIG. 1 represent an average machinability. Hence, the incorporation of micas into ceramics facilitates machining while enhancing its strength and toughness, thus decreasing machining cost and improving the possibilities of obtaining chip-free material. The utilization of chip-free materials enables the obtainment of more precise machining tolerances at the edges and corners of the materials. This is possible because the present mica/ceramic material due to its enhanced strength and toughness is less susceptible to brittle failure.

The unique and new idea involved in this invention of a new family of materials is the use of synthetic fluorine micas as a dispersed second phase incorporation in a ceramic body producing a particulate dispersion composite or a dispersed mice-laminate to:

(a) toughen ceramic material thereby enhancing strength,

(b) control mechanical, electrical, chemical properties,

etc.,

(c) improve thermal shock resistance,

(d) implement self-lubrication enhancement.

degree of particularly, it is understood that the present disclosure has been made by way of example and that other operable ceramics and synthetic fluorine containing micas and methods of fabrication thereof will occur to a person of ordinary skill in the art.

Having described my invention, I claim:

1. A hot-pressed composition of matter consisting of a ceramic material having incorporated therein a fluorine containing mica component as a dispersed phase in an amount of to 50% by volume, wherein the ceramic is selected from the group consisting of A1 0 MgO,

3A1203 Slog,

Si N and SIG- and wherein the mica is selected from the group consisting of KMg AlSi O F and BaMg Si O F 2. A hot-pressed composition of matter in accordance with claim' 1, wherein the ceramic is A1 0 and wherein the mica is .BaMgAlsi o F 'z' References Cited UNITED STATES PATENTS 3,789,096

1/1974 Church et al. 264- 3,141,786 6/1961 Bugosh 10673.1 X 3,122,505 2/1964 Rulon-Miller et al. 252-12 3,291,622 12/1966 Mandorf 10673.1 X 2,897,573 8/1959 Hessinger 106Dig. 003 2,859,794 11/1958 Barr l0673.5 X

OTHER REFERENCES Rossi et al.: Final Stage Densification in Vacuum Hot- Pressing of Alumina, J. Am. Cer. Soc., 48 (11), 1965, pp. 558-64.

Comeforo et al.: Synthetic Mica Investigations: I Hot- Pressed Machinable Ceramic Dielectric, J. Am. Cer. Soc., 36(9), 1953 (pp. 286-394).

HELEN M. MCCARTHY, Primary Examiner us. 01. X.R.

51308; l0639.5, 73.1, 73.4, 73.5, Dig. O03; l6l17l; 252-12; 264- 

